Perhaps 'everything' but I doubt that. I reason from observation of life that many things happen in ways that support existence of intentionality. There's growth and seasons of development repeated in living things and their systems; internally and externally. There is the symphony of commonly shared life paradigm: Tension/Charge/Discharge/Relaxation in both animate and inanimate planetary phenomena. To pretend to 'know' how it all operates and why is as juvenile as claiming to be a prophet for some god or other. It is very arguably in operation though.

It takes to much to think about this, unless one is just trying to be funny. There are so many ways to answer this. I do not judge people by what they say as many times something has to be said before one sees how stupid it sounds and is. Apparently shit does not just happen.

I normally don't engage with people with those thoughts...however on one of my dating sites they ask about it and I say in response, "what's the reason that little kids are born into starvation in India?" They don't like that one.

I change the subject!

"Everything happens for a reason", when uttered by some people seems to imply some vague elevated mystical status. If they were honest they might say, fucked if I know.

Like we say in Italy and Greece , “ donkeys can fly “
The response is : “ u are right , I seen one flying yesterday indeed “.
Doesn’t matter to me regardless if the person that I am taking with is a good friend or a fair weather friend . I don’t argue anymore ,. Until : if their rationale is to promote or endure abuse / injustice / crime . Then , that’s a different animal . If rested and have time , I won’t let them have it easy . If already tired and fed up , most likely will be a ear full response . Cussing included . Such a classy lady I am .

I think most people say it without really thinking about whether it's true or not, because it SOUNDS good, and doesn't cost anything.
It's like telling someone, "I'll pray for you," because it allows them to feel good about themselves without requiring them to actually DO anything.
And when you think about it it's true. For instance, a meteor crashes into your house. The reason? It travelled through space and it's path just happened to hit Earth at your houses' coordinates.

Yes it is called cause and effect, no god required.

Isn't it one of those lines/cliches people casually use in conversations? It's not worth dwelling on such a cliche, let alone judging people because they use it. I would probably just continue with the conversation I'm engaged in.

I don't give it much thought anything people say.

I view it as a time to smile and be quiet.

Humans use everything we experience to form an opinion of what's real and, therefore, what pathways to tread along. More things will naturally happen (because life isn't static) along the way which relate to the original experience so it seems to have a "reason" for happening. Nothing odd in that. Creating an illogical idea involving some intelligent Being directing events in our lives from such an experience seems to miss the saner aspect of philosophy. All that said, I merely say that I don't believe an intelligent source directed us into a path and leave it at that. If they want to explore an alt idea then I determine how much time I have or how much I care about this nitwit.

Always polite unless they are belligerent

I agree with @Willow_Wisp and @Barnie2years, and I'm usually polite. I know a lot of people with different viewpoints than mine so unless they're trying to impose them on me, I let it slide.

I don't know that I judge them, but I note in my head that there are certain topics to tread gently around ... or not, depending upon the circumstances.

I just know it's true, but not in the way they would like to think it's true.

Doesn’t bother me unless they try to put a god spin on it. Realistically, everything does happen for a reason: you were stupid, careless, wrong place wrong time, born into a good family, very smart…. The list is endless, but some ephemeral being is not one of the reasons.